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Reasons Behind HVAC Motor Failure in Your BMW


With the unofficial start to summer coming this weekend, we are sure to need our air conditioners soon, if we haven’t had to use them already.  Your BMW has an incredibly high-quality climate control system that runs both your heat in the colder months and the air conditioning when it's hot outside.

With the warmer weather, you might find that your climate control system isn’t working up to par. Perhaps it wasn’t working on the cold days either. There’s nothing worse than having a state of the art climate control system that simply blows air into your car that is the same temperature as the air temperature outside of your car.

HVAC stands for Heating Ventilating and Air Conditioning, which is your climate control system. Let's look at some of the reasons behind your HVAC motor failure and where to go for help. Throughout this article, we’ll use the terms HVAC, HVAC System, air conditioning, and climate control system interchangeably. We are referring to the system that heats and cools your BMW.

Finding the Problems With Your HVAC Motor

Before we know what is causing the problems with the HVAC system, we have to first diagnose the problem. There are things you can do manually at home if you wish to know what is happening. However, they can be completed more easily in a professional garage using a differential diagnosis computer system.

Should you want to do this manually, here are the steps. It’s not complicated, but it does take a little bit of time. First, from inside your car and with your car running, turn on the air conditioner to its highest setting. If your car has a max air conditioning setting, use that. Make sure that the circulating air is set to outside circulating, not inside recirculating. Make sure your windows are rolled up. You should also have a pen and notebook to write down your findings. This diagnosis process will help you determine what part of your HVAC system needs to be replaced or repaired. Once you have found a problem, or you have found your first “finding,” continue with all of the checks. There could be more than one issue with your HVAC system.

HVAC Air Pressure

Adjust the blower from low to high. Pay attention to the change in the air pressure. Try changing the blower from high back to low and then back to high, but stop on each mark. Is there a noticeable change in the air pressure as you change the blower speed?

If the air pressure is low and doesn't change, but the temperature is cold, you likely have a bad filter in the HVAC system. Another common problem is faulty blower motor resistor. This would cause the blower to change pressure sporadically or to simply stay on the same pressure all the time, regardless of whether you adjust the blower speed.

HVAC Air Temperature

Next, let’s check the temperature of the air coming out of the vents. The temperature of the air coming out of the HVAC system in your car is another indicator of what is wrong with your HVAC system.

  • If the air is cool but not cold, and the air pressure is consistent, you likely have a problem with your radiator, a clogged filter, or a cooling fan problem.
  • If the air is cold at first and then gets warm after your car has been running, you likely have a leak in the HVAC compressor. Also, there could be a leak the hoses of the HVAC system.
  • Another possibility, if it’s not a leak in the HVAC system, you could have a faulty compressor clutch. The compressor clutch keeps a set pressure in the HVAC system. The compressor clutch is used every time the HVAC system is cooling your BMW.  A leak in the hoses of the HVAC system presents the same symptoms as that of a faulty compressor clutch. An expert service technician at DART Auto will be able to properly diagnose the issue for you.
  • If you turn on the HVAC system to blow cold air but you feel warm or hot air instead, this is likely due to a loss of refrigerant in the HVAC system. It’s also possible that the compressor has frozen up. The compressor is usually between the radiator and the engine, so if the compressor is not working but the air is still moving through the coils and then into your car, they could be pulling the heat from the car’s engine in through the vents.

Sounds from the HVAC Systems

When you turn on your HVAC system, it should be relatively quiet. You might hear some of the air movement through the vents. Even then, it shouldn’t be too terribly loud. If you hear a rattling sound, it is most likely the compressor. The compressor will rattle when it first starts to fail.

Another sound you might hear is a grinding or squealing noise. This can happen if the compressor pulley bearings are starting to fail or have failed. Once a compressor or pulley begin to fail you want to get them fixed right away. They will only get worse with continued use.

Repair Your Car’s AC System at DART Auto

HVAC problems can be hard to diagnose and challenging to fix.BMW_AC_Servicing.jpg At DART Auto, every service specialist is a factory-trained and certified technician. The service specialists are experts on BMWs and will know how to fix your HVAC system. DART Auto is located in Denver and serves the communities of Englewood, Littleton, Centennial, and Denver, CO. Please give us a call or stop in. We know you want the best, and we can’t wait to show you that we are the best at servicing European cars.